A family history of low bone mass is a risk factor for the development of osteoporosis but the mechanisms responsible for this finding are not know. The potential for a family history of low bone mass to alter calcium metabolism may be most apparent in young girls because the majority of bone mass is obtained prior to the age of 16 years in females. The goals of this study are to determine if young girls from families with histories of osteoporosis have alternations in their ability to absob calcium and deposit it into bone. For three weeks before each clinical study, each girl consumes a high calcium diet chosen to provide the amount of calcium which is currently being recommended for adolescent girls. On the day of each study two special forms of calcium tracers are given to each girl so that we can follow the clearance of calcium into bone over the following 5 days. To date,we have completed the clinical study in 3 girls from families with strong histories of osteoporosis, and 7 more girls will be recruited for this study. Although it is too early to comment on our results, this information will provide useful information on the recommendations for children from osteroporotic families.